Tech Tip of the Week | Encks Auto Repair By Paul Enck | Call: 727-822-1
Diesel vehicles have a loyal following but finding a shop that actually works on them is not always easy. Encks Auto Repair is one that does — and this week Paul walks through a real diesel that came in with a misdiagnosed leak that turned out to be something most owners would never have suspected.
The customer brought the vehicle in complaining of a diesel smell and what they believed was a fuel leak. After inspection Paul found something different entirely.
“It turns out it was an oil leak coming from the fuel injection pump right here — which sits all the way down in the center between the heads behind the timing cover. The customer thought he had a rear main leak. Actually it was this pump that was leaking.”
— Paul Enck, Encks Auto Repair
The injection pump on this engine sits deep in the valley between the cylinder heads and runs off the main oil pump. Oil was leaking externally from the pump, running down toward the rear of the engine, and giving every appearance of a rear main seal leak — a much more involved and expensive repair.
Getting the correct diagnosis before authorizing work saved the customer from paying for the wrong repair.
Diesels are durable but they require consistent maintenance — especially in a harsh, hot climate where heat and dust accelerate wear on filters and injectors.
“Diesels require maintenance too. In this harsh climate we live in, usually it’s an injector or a filter. Keep them serviced every 5,000 miles.”
— Paul Enck, Encks Auto Repair
Oil changes — every 5,000 miles
In hot and dusty conditions, stretching oil change intervals on a diesel is not worth the risk. Every 5,000 miles keeps the oil clean and the injection pump — which relies on oil pressure to function — properly lubricated.
Fuel filters — every other oil change
Diesel fuel filters work harder than most drivers realize. They protect the injection system from water, sediment, and contaminants that can destroy injectors.
“Have your fuel filters changed every other oil change — so about every 10,000 miles. Unless you get a bad load of diesel, that’s fine for these engines.”
— Paul Enck, Encks Auto Repair
A bad load of diesel — contaminated or water-laden fuel — is a reason to change the fuel filter sooner rather than waiting for the next scheduled interval.
Pro Tip: If you ever notice a diesel smell inside or outside the vehicle, do not assume it is a fuel leak before having it properly diagnosed. As this Tech Tip shows, the source can be something entirely different that only a thorough inspection will reveal.
1. How often should a diesel be serviced?
Every 5,000 miles in hot or dusty climates is Paul’s recommendation. Diesel engines are built to last but they depend on clean oil and filters to protect the injection system and internal components from premature wear.
2. How often should diesel fuel filters be replaced?
Every other oil change — approximately every 10,000 miles under normal conditions. If the vehicle has been filled with a bad load of contaminated or water-heavy diesel, change the filter sooner regardless of mileage.
3. What does the fuel injection pump do on a diesel engine?
The injection pump pressurizes and delivers fuel to the injectors at precisely timed intervals. On many diesel engines it also relies on engine oil pressure to operate correctly, which means oil quality and pressure directly affect injection system performance.
4. What are the symptoms of a failing diesel fuel injection pump?
Hard starting, long crank times before the engine fires, rough running, loss of power, excessive smoke from the exhaust, and in some cases a diesel or oil smell depending on what type of leak has developed. Any of these symptoms warrant a professional inspection.
5. Can a diesel injection pump leak oil instead of fuel?
Yes, as Paul’s example demonstrates. The injection pump on many diesel engines runs off the main oil pump and can develop external oil leaks that are easily mistaken for leaks from other components. Proper diagnosis is essential before any repair is authorized.
6. What happens if the fuel filter is not changed on a diesel?
A restricted fuel filter starves the injection system of clean fuel, forcing the injection pump to work harder and reducing its lifespan. Contaminated fuel that bypasses a clogged filter can damage injectors, which are expensive to replace — often several hundred dollars per injector.
7. Are diesel injectors expensive to replace?
Yes. Diesel injectors are precision components and replacement costs can run from 200 to 600 dollars per injector depending on the engine. Keeping fuel filters clean and using quality diesel fuel is the most effective way to protect them.
8. What is a bad load of diesel and how do I know if I got one?
A bad load refers to diesel fuel that is contaminated with water, sediment, or microbial growth. Signs include rough running shortly after refueling, loss of power, hard starting, or a fuel filter that turns dark and restricts quickly after a recent change. If you suspect a bad load, change the fuel filter promptly.
9. Do diesels need the same general maintenance as gasoline engines?
Many items are the same — oil changes, air filters, belts, hoses, and cooling system service all apply. The key differences are the fuel system components — fuel filters, injectors, and the injection pump — which require specific attention and more frequent filter changes than a gasoline fuel system.
10. Why is it hard to find a shop that works on diesels?
Diesel diagnosis and repair requires different tools, training, and experience than gasoline engine work. Injection system diagnosis in particular involves specialized equipment that not every general repair shop invests in. Finding a shop with genuine diesel experience — like Encks Auto Repair — matters when the diagnosis needs to be accurate the first time.
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